Polymeric color formers and process of preparing same



nited States Patent US. Cl. 2608 4 Claims ABSTRACT OF THE DISCLOSUREProcess for making polymeric color formers by polymerizing at C.-90 C. amixture of 1) aqueous gelatin,

(2) an addition polymerizable monomeric color former containing anactive color former nucleus capable of forming quinoneimine orazomethine dye, and

(3) an addition polymerizable vinyl compound that is liquid at 50 C.,

and the color formers resulting from the process. The color formers havegelatin-like characteristics and are nonmigratory, free of haze, formtough elastic layers and have a low coefiicient of friction.

This application is a division of prior application Ser. No. 398,738filed Sept. 23, 1964, entitled Color Formers now patent number3,370,952.

This invention relates to a new class of non-migratory polymericcolor-formers and to photographic silver halide emulsions containingthese color-formers.

It has long been recognized that, in multilayer, color photographicfilms, it is necessary that the various colorforming compounds in theseparate layers should, desirably, be made as non-migratory as possiblein order to minimize color contamination and to reproduce the colorbalance of the original subject as accurately as possible. Variousmethods of achieving this objective have been employed, e.g., the use ofpolymeric color-formers, colorformers with attached long-chain alkylradicals, mordanting techniques, etc. Among the problems that havearisen have been inadequate non-migratory properties of thecolor-former, incompatibility with the gelatin binder, and lack offlexibility of the elements.

An object of the present invention is to provide a new class ofcolor-forming polymeric materials which have excellent non-migratoryproperties. A further object is to provide such color-formers which arecompatible with gelatin, which are water-soluble or water-dispersibleand which are suitable for use as all or part of the binder in aphotographic silver halide emulsion. Still another object is to providecolor-forming polymeric materials from which photographic coatings andelements having excellent flexibility may be prepared. Still furtherobjects Will be apparent from the following detailed description ofinvention.

The color-forming materials of the present invention are Water-solubleor water-dispersible film-forming polymers prepared by a process whichcomprises polymerizing by heating to a temperature of 25 C. to 90 C. fora period of 1 to 36 hours, a mixture comprising (1) aqueous gelatin; (2)an addition polymerizable monomeric color former of the formula:

3,444,110 Patented May 13, 1969 ice where R is a member selected fromthe group consisting of hydrogen; alkyl of 1-4 carbon atoms; chlorineand bromine; R' is a divalent organic radical and Q is an active colorformer nucleus capable of forming upon chromogenic development ofexposed silver halide images with a primary aromatic aminecolor-developing agent, a dye selected from the group consisting ofquinoneimine and azomethine dyes, said nucleus, in an enol form, havingthe formula:

=1: is :(JH, JCl, =CJBr, =I I, or JSO;H dissolved in (3) an additionpolymerizable vinyl compound that is liquid at 50 C., the gelatin,monomeric color former and polymerizable non-color forming monomer beingpresent in parts by weight of 10 to 90, 3 to 75, and 2 to 60,respectively.

The foregoing active color forming nuclei are found in the reactivemethylene dye intermediates and in aromatic hydroxyl compounds andinclude the reactive ethenol groups. These groups occur in phenols,naphthols, acylacetamides, cyanoacetals, betaketo esters, pyrazolones,homophthalimides, coumaranones, indoxyls, thioindoxyls, and indazolones.

The invention is also concerned with photographic silver halideemulsions wherein the gelatin-compatible colorforming polymeric materialcomprises at least 50% by weight of the silver halide binder.

An important class of suitable monomeric color-formers are disclosed inFirestine, US. 2,976,294, issued Mar. 21, 1961, wherein the divalentradical R, represents the amido group CONH. In this patent, it isdisclosed that Q is an organic radical which contains an acyclic orintracyclic active methylene group, the active methylene group (CH beingrendered mobile by the proximity of certain activating groups, forexample,

and others. I

The CH group is usually present between two such groups in a cyclic oracylic system. It should be noted that that 'formula above for Q iswritten in the enol form wherein the active methylene. group has thestructure =CH. Suitable monomeric color-formers are also disclosed inassignees co-pending application of Umberger, Ser. No. 113,101, filedMay 29', 1961. The monomers disclosed in this application are vinylether monomers of the formula wherein Z is hydrogen or methyl. Yetanother class of suitable color-forming monomers are disclosed inFirestine et al., Patent 3,163,625, Dec. 29, 1964 (US. Ser. No. 21,959,filed Apr. 13, 1960), wherein there are disclosed monomers of thestructure wherein R is an aromatic hydrocarbon radical or an organicradical of aromatic hydrocarbon character and R is a member selectedfrom the group consisting of hydrogen, alkyl of 14 carbon atoms, andchlorine.

The suitable non-color-forming monomers are those which willcop-olymerize efficiently with the color-forming monomers in thepresence of gelatin and, also, act as liquid solvents for thecolor-forming monomer. These include essentially any readily availablevinyl monomers, the preferred compounds being those which are the bestsolvents for the color-forming monomer. The invention is operable evenwhen the vinyl monomer will dissolve only a limited amount of thecolor-former. The better the solvent action of the non-color-formingmonomer, the less is required and, therefore, the more concentrated incolor-former is the polymer which is formed. Particularly usefulnon-color-forming monomers are the low melting, non-ionized, syntheticvinyl monomers such as the alkyl acrylates and alkyl alkacrylates (e.g.,alkyl methacrylates) where alkyl represents radicals of 1 to 8 carbonatoms. Other useful monomers are the vinyl esters such as acetate,propionate, etc., vinyl and vinylidene halides such as vinylidenechloride, styrene and substituted styrenes, the dienes such as thepentadienes, hexadienes, etc., acrylonitrile, methacrylonitrile, and thelike.

In carrying out the polymerization reaction it is desirable to use freeradical initiators such as his azo initiators or redox initiatorsystems. Suitable bis azo initiators include:

Suitable redox initiator systems include ammonium, sodium, or potassiumpersulfate in combination with sodium metabisulfite, sodium sulfite,sodium thiosulfate, or sodium phosphite.

Also, it is desirable, to employ a surfactant during the polymeriztionreaction. Anionic surfactants are preferred, especially sodium laurylsulfate. Other useful anionic surfactants include dodecylbenzenesulfonic acid, naphthalenesulfonic acid condensed into a polyanion withformaldehyde, sodium isopropylnaphthalene sulfonic acid and sodiumdioctylsulfosuccinate. Useful amphoteric surfactants are those disclosedin Nottorf, US. Patent No. 3,142,568, July 28, 1964 (e.g.,alkylimino-dicarboxylates), as well as other amphoteric compounds suchas bet'aine (e.g., C-cetyl betaine, taurines', glycines, etc.).

The color forming modified gelatins are particularly useful inmultilayer color films such as described in Chu et al., U.S.P.3,211,552., Oct. 12, 1965 (Ser. No. 113,100, filed May 29, 1961). Thethin layers described therein are particularly advantageous in obtaininghigh definition images. These color-forming modified gelatins may beused in any or all of the record layers of such multilayer films and mayserve as the sole silver halide binder or may be mixed in variousproportions with gelatin or other compatible binding materials. Forexample, it may be desirable to use cyan color-forming modified gelatinas the only color-former in the red record layer but to use magenta andyellow colorforming polymers such as described in US. Ser. No. 113,100above in the green and blue record layers of a multilayer colorphotographic film.

The multilayer color films of this invention are processed in aconventional manner. Colors are formed by development with an oxidizedcolor developer, e.g., an aqueous alkaline developer solution of thetype disclosed in Example I of Jennings, US. Pat. 2,397,865, Apr. 2,1946. However, any of the other color-developing agents described insaid Jennings patent can be used.

The invention will be further illustrated by but is not intended to belimited to the following examples.

of Starting materials were g latinlcolor-former-monomer/ methylacrylate==75/8/ 17.

Materials Gelatin l-hydroXy-N-(fl-vinyloxyethyl)-naphthamide (cyancolor-former monomer) Amount, g. 225

The gelatin was dissolved in 2000 ml. of water in a reaction flask fromwhich air had been purged with nitrogen. After adding sodium laurylsulfate, the solution was stirred for several minutes and then heated to60 C.

The cyan color-forming monomer was dissolved in the ethyl acrylate at 50C. and the solution charged to the reaction flask.

The ammonium persult'ate and the sodium metabisulfite were thendissolved in separate portions of the balance of the water and added tothe reaction mixture. Polymerization began as soon as the catalystsolutions were added and was completed by heating the reaction for 3-4hours at 60 C. The product was a tan colored viscous liquid that set toa gel at room temperature. It was soluble in warm water in allproportions.

The product had a yield of 3,225 g., a percent solids of 10.85, a pH of4.90, and a viscosity at 40 C. of 130 cps. This product was used as partof the binder of a silver halide photographic emulsion. After coating ona support, exposing to light in a camera and developing in acolor-developer (para-amino diethyl aniline hydrochloride), a cyancolored image of good saturation and good resolution was obtained. Thefilm had a high gloss and was free of haze.

EXAMPLE II Another cyan color-forming modified gelatin was preparedusing a ratio by weight of starting materials such thatgelatin/eolor-former monomer/ ethyl acrylate=== /8/17.

The polymerization was conducted under a nitrogen atmosphere in a twoliter reaction flask. The gelatin was soaked for 15 minutes in 800 ml.of cold distilled water in the reaction flask and then stirred tosolution at 60 C. Air was displaced from the flask by a steady stream ofnitrogen.

The color-former monomer was pulverized finely and dispersed in asolution of the sodium lauryl sulfate in 50 ml. of water. Thisdispersion was added to the gelatin solution in the reaction flask whilestirring. The initiator, azobisisobutyronitrile, was dissolved in thedeinhibited ethyl acrylate and this solution was charged to the reactionflask. The reaction mixture was stirred for 24 hours at a temperature of60-80 C. while nitrogen was used as a constant purge. During this periodthe course of polymerization was observed by the change in appearance ofthe reaction mixture from a cream colored, opaque dispersion at thebeginning to a bluish white, translucent, viscous solution at the end.On cooling, the solution set up as a firm gel.

This product was found to possess 11.7% by weight solids. It was dilutedto a 5% solids solution with water and coated on a polyester film baseas described in Example IV of US. Patent 2,779,684. It dried to a clearlayer having good anchorage to the film base. When a sample of coatedbase was immersed in a solution of a para amino diethylaniline colordeveloper to which a few crystals of potassium ferricyanide had beenadded a brilliant cyan color developer in -12 seconds.

EXAMPLE III A cyan color-forming modified gelatin was prepared using aratio by weights of starting materials such that gelatin/color-formermonomer/acrylonitrile=75/ 8/ 17.

Materials: Amount Gelatin g 75 l-hydroxy-N-(fl-vinyloxyethyl)-naphthamide g 8 Acrylonitrile g 17 Sodium lauryl sulfate (30% by weightaqueous solution) g 50 Ammonium persulfate g 2 Sodium metabisulfite g 1Distilled water ml.. 900

The reaction was carried out in a 3 liter flask in an atmosphere ofnitrogen.

The gelatin was soaked for min. in 830 ml. of cold distilled water andthen stirred and heated to solution at 40 C. Then the sodium laurylsulfate was diluted with 50 ml. distilled water and added to the gelatinsolution. The color-former monomer was dissolved in the acrylonitrile at40 C. and added to the reaction mixture, followed by additions of theammonium persulfate and the metabisulfite. The reaction mixture washeated 20 hours at 40-50 C. and the product was obtained as a turbidsolution that formed a gel on cooling to room temperature. The solidscontent was 9.8% by weight.

A solution, diluted with distilled water to a solids content of fivepercent, dried down to a frosty layer when coated on the film base ofExample II. The coating developed to a cyan color when immersed in anoxidized solution of the photographic color developer,para-aminodiethylaniline.

EXAMPLE IV A cyan color-forming modified gelatin was prepared using aratio by weights of starting materials such that gelatin/color-formermonomer/butylacrylate=43/ 14/43.

Materials: Amount, g. Gelatin 751-hydroxy-N-(B-vinyloxyethyl)-naphthamide The reaction was carried outin a 2-liter glass reaction flask in an atmosphere of nitrogen.Seventy-five grams of gelatin was soaked 15 min. in 800 ml. of colddistilled water in the reaction flask and then warmed with stirring to40 C. During this time the flask was purged with nitrogen gas. Aftersolution was complete, the sodium lauryl sulfate was added to the flaskwhile rinsing it with 25 ml. of distilled water.

The cyan color-former was dissolved in the butyl acrylate at 40-50" C.and this solution was also charged to the flask, along with theazobisisobutyramidine hydrochloride which was dissolved in 25 ml. water.

Polymerization was accomplished by heating the reaction mixture whilestirring to 70 C. at which temperature an exothermic reaction tookplace, raising the temperature to 82 C. for several minutes. Thetemperature was then maintained for 4 /2 hours at 75 C. to assurecompletion. The product was a translucent gel with a bluish-white color(other times the product has been made with a pinkish color) and wasfound by analysis to have 17.0% solids. A solution of the product wasprepared by diluting with water to 5% solids and the solution was coatedon a polyester film base. The dried coating gave an intense (blue) colorwhen immersed 3-4 minutes in a photographic color developer solutioncontaining several crystals of potassium ferricyanide.

EXAMPLE V A yellow color-forming modified gelatin was prepared using aratio by weights of starting materials such that gelatin/color-formermonomer/ethyl acrylate=/ 8/ 17 Sodium lauryl sulfate (30% by weightaqueous solution) g 150 Sodium metabisulphite g 3 Ammonium persulphate g6 Distilled water ml 2700 The polymerization was conducted in a 5-literreaction flask in an atmosphere of nitrogen in accordance with thefollowing procedure.

The gelatin was soaked in 2000 ml. of water in a 5-liter reaction flaskfor 15 minutes. The air was purged by maintaining a steady flow ofnitrogen throughout the reaction period. At the end of the soakingperiod the agitator was started and the mixture was warmed to 40 C. toeffect solution. The sodium lauryl sulfate, diluted 'with 200 ml. 11 0,was added and rinsed with ml. of water.

Next were added the ammonium persulphate and the sodium metabisulfite,each dissolved in 100 ml. of water. The yellow color-former monomer,dissolved in the ethyl acrylate at 50 C., was next added to the reactionvessel. Finally, the persulfate and metabisulfite solutions were addedand each was rinsed with 100 ml. of water. The temperature of thereaction mixture was raise-d to 60 C. and held at that temperature i2 C.for 3 hours. The product obtained was a yellow gelatinous compound whichwas coated, after dilution with water to 5% solids, on the film base ofExample H, to give a colorless transparent layer. When a sample of baseso coated was immersed for 3 minutes in a photographic color developersolution, to which had been added a few crystals of potassiumferricyanide, a yellow color was developed.

EXAMPLE VI A magenta color-forming modified gelatin was prepared using aratio by weights of starting materials such that gelatin/color-formermonomer/ethyl acrylate:

Materials: Amount Gelatin g 225 1-phenyl-3-methacrylamido-5-pyrazolone g24 Ethyl acrylate g 51 Sodium lauryl sulfate (30% by weight aqueoussolution) g Ammonium persulphate g 6 Sodium metabisulfite g 3 Distilledwater ml 2700 This color-forming modified gelatin was prepared by theprocedure used in Example V.

The product was a tan colored gelatinous material which could be coatedas a 5% solids solution on the film base of Example II to give a cleartransparent layer. This coating, when immersed for 3 minutes in aphotographic color developer solution in which several crystals ofpotassium ferricyanide had been added, developed a deep magenta color.

EXAMPLE VII A magenta color-forming modified gelatin was prepared usinga ratio by weights of starting material such that gelatin/color-formermonomer/ethyl acrylate:

Materials: Amount, g. Gelatin 75 1-phenyl-3-methacrylamido-S-pyrazolone8 Azobisisobutyronitrile 1.0 Ethyl acrylate 17 Sodium lauryl sulfate byweight aqueous) Distilled water The polymerization is carried outsimilar to the pro cedure described in Example II. The product was aclear, straw colored gelatinous material which was coated on the filmbase of Example II to give a clear layer. On development in an oxidizedphotographic color developer solution, a clear, intense magenta colorwas formed.

EXAMPLE VIII A gelatino-silver halide emulsion, prepared for coating inthe normal manner, was divided into two equal portions containing 0.033mole of silver halide each. To one portion there was added 140 g. of thecyan color-forming modified gelatin described in Example II (a gelcontaining 11.7% solids prepared from starting materials having weightratios of gelatin/cyan color-former monomer/ ethylacrylate=75/ 8/ 17).To the other portion, serving as control, there was added a cyancolor-forming copolymer of maleic anhydride andl-hydroxy-N-(beta-vinyloxyethyl)-2-napthamide, prepared as described inExample I of assignees copending application of Umberger, Ser. No.113,101 filed May 29, 1961. Gelatin was also added to the controlemulsion to compensate for that which was present in the color-formingmodified gelatin so that both emulsions had about the same finalconcentration of gelatin as well as cyan color-forming nuclei.

The two emulsions were coated on photographic film base, dried andprocessed as color-reversal films in the conventional manner. It wasobserved that the processed coating containing the modified gelatin hada very high surface gloss. Absorption curves of the developed dyes fromthe two coatings were compared in a Cary Recording SpectrophotometerModel 14MS, Serial 14 (Applied Physics Corp., Pasadena, Calif.), and nosignificant dif ferences in absorption maxima were observed.

Relative brittleness (flexibility) values of the two films werecompared, both with processed and unprocessed samples, by pulling thesamples through a brittleness test wedge to determine crackingdiameters. The procedure employed was that described in ASA Standard PH1.3 1-19S 8. The following values of cracking diameters were thendetermined with diameters given in centimeters:

Film containing color-former modified gelatin:

Processed 0.21

Unprocessed 0.13 Control film:

Processed 0.43

Unprocessed 0.27

The smaller values of cracking diameter, of course, indicate greaterflexibility.

EXAMPLE IX An essentially identical coating of the gelatino-silvcrhalide emulsion containing the cyan color forming modified gelatin ofExample VIII was used as the first layer on a multilayer film element.Over this first layer on a suitable film base there were coated insuccession:

(a) A separator layer comprised of a solution of bone gelatin containingsaponin as a surfactant and chromealum as a hardener;

(b) A gelatino-silver bromo-iodide emulsion layer sensitive to blue andgreen light and containing a polyanion pyrazolone magenta color-formercopolymer of the type shown in Firestine et al., US. Patent 3,163,625,Dec. 29, 1964 (U.S. Ser. No. 21,959 filed Apr. 13, 1960).

(c) A gelatin layer containing colloidal silver for absorbing bluelight;

((1) A gelatino-silver bromo-iodide emulsion layer sensitive to bluelight and containing a polyanion benzoylacetanilide yellow color-formerprepared by transacetalization of low viscosity 99% hydrolyzed polyvinylalcohol with m-benzoylacetamidobenzaldehyde ethylene glycol acetal ando-sulfobenzaldehyde in an ethanol-water reaction medium withp-toluenesulfonic acid as acetaliza tion catalyst; and

(e) A gelatin antiabrasion layer.

A sample of the completed multilayer film was exposed in a camera andprocessed by reversal with all solutions being at 70 F. The film wasfirst developed in a conventional black and white, p-methylaminophenolhydroquinone developer, then treated in an acid shortstop bath, waterwashed, and re-exposed by flashing to white light. It was then colordeveloped for 20 minutes in a solution containing ten grams per liter ofthe developing agent, 4-amino Nethyl-N(beta-methanesulfonamidoethy1)-m-toluidine sesquisulfatemonohydrate, 40 grams per liter Na PO -12H O, and 20 grams per literanhydrous Na SO Processing was continued with treatment in another acidshortstop bath, washing with water, bleaching, washing, fixing withsodium thiosulfate, washing and drying. A good positive multicolortransparency was obtained.

Although this invention is particularly applicable to negative andreversal color films which are designed for exposure in a camera, it isalso useful in other color films which may have other than theconventional layer arrangements. The emulsions of this invention can beused advantageously in negative, positive or reversal color films whichmay be for cine or still use, in transparencies, prints for viewing byreflected light, intermediate films, etc.

The light-sensitive emulsion layers may be arranged with respect to thesupport in other manners and with other arrangements of spectralsensitivities and colorformers as is known in the art. Suitable otherlayer arrangements are disclosed in US. Patents 2,397,864, 2,927,019,2,927,024 and 2,997,338.

The invention, moreover, is not limited to the specific light-sensitivematerials described in the above detailed examples. Various other simpleand mixed silver halides may be used as the light-sensitive materials inlike manner. Mixtures of silver bromides, chlorides, and/ or iodides canbe made by adding mixtures of soluble salts of these halides in likemanner. Other useful soluble halides include calcium bromide, potassiumiodide, sodium and potassium chlorides and iodides, etc.

Inert ingredients, e.g., pigments, colloidal silver, matting agents,etc. may be present in all of the element layers including the support.The element may also contain chemical sensitizers, optical sensitizers,coating aids, antifoggants, non-halation dyes and pigments, brighteningagents as known to the art, etc.

The color-forming modified gelatin may be used as the sole binder or maybe used in combination with gelatin since it is compatible with gelatinin all proportions. The color-forming modified gelatin can also be usedin combination with other natural or synthetic water-permeable organiccolloid binding agents. Such agents include polyvinyl acetal of sodiumo-sultobenzaldehyde; various polysaccharides, e.g., dextran; thehydrophilic copolymers in Shacklett, US. Patents 2,846,411 and2,834,758; polyvinyl pyrrglidone, and polymers of acrylamide andmethacrylam e.

The emulsions can be coated on any suitable support, e.g., celluloseesters, cellulose mixed esters, superpolymers, e.g. poly(vinyl chlorideco vinyl acetate), polyvinyl acetals, butyrals; polystyrene; polyamides,e.g., polyhexamethylene adipamide, polyesters, e.g., polycarbonates,polyethylene terephthalate, polyethylene terephthalate/isophthalate,esters formed by condensing terephthalic acid and its derivatives, e.g.,dimethyl terephthalate with propylene glycol, diethylene glycoltetramethylene glycol, eyclohexane-l, 4-dimethanol (hexahydro-p-xylenedialcohol); paper, metal, glass, etc.

Elements made up of integral coupler emulsions obviously become moresusceptible to interlayer color contamination (particularly thecontamination due to migration of oxidized developer during the colordevelopment step) as the emulsion layers become thinner. It has beenfound that this color contamination can be effectively reduced by theaddition of a competing coupler, e.g., phenols that form a solubleremovable dye on coupling (such as citrazinic acid). In particular, ithas been found that larger than normal concentrations of sodium sulfitein the color developer solutions are especially effective in combinationwith the color-former modified gelatin in reducing interlayer colorcontamination caused by migration of oxidized developer and by migrationof colorformer molecules.

In the case of integral color films, the color-forming modified gelatinis, of course, incorporated in the film element.

An advantage of the invention is that the color-forming modifiedgelatins have gelatin-like characteristics and may be easilyincorporated into silver halide emulsions as total or partialreplacements of gelatin. The color-former substituent is etficientlycoupled by the color developer and there is some evidence to suggestthat the color-forming modified gelatins are significantly more activein color development reactions than conventional color-formers. Inmultilayer color films it has been found that color contamination is ata remarkably low level due to the nonmigratory nature of these novelcolor-formers. Also, the use of color-former modified gelatins leads tomultilayer films which have reduced tendency to crack or break when usedin cameras or projectors, i.e., the films are more flexible.Furthermore, such films have low curl, and they are tough and elasticeven at low temperatures. Color film layers containing the materials ofthis invention are clear, free of haze and have a very high surfacegloss. Because the silver halide grains of a color emulsion made withcolor-forming modified gelatin are uniformly and intimately surroundedby the color-forming groups, which have low light scattering effects,the colored image obtained is sharp and well defined. Another advantageis the low coefilcient of friction of the films of this invention. Stilladditional advantages will be apparent from the above description of theinvention.

The embodiments of the invention in which an exclusive property orpriviledge is claimed or defined as follows:

1. A process for making polymeric color formers which comprisespolymerizing by heating to a temperature of 25 C. to 90 C., a mixturecomprising 10 (1) aqueous gelatin; (2) an addition polymerizablemonomeric color former of the formula:

R H,C=( JRQ where R is a member selected from the group consisting ofhydrogen; alkyl of 14 carbon atoms; chlorine and bromine; R is adivalent organic radical and Q is an active color former nucleus capableof forming upon chromogenic development of exposed silver halide imageswith a primary aromatic amine color-developing agent, a dye selectedfrom the group consisting of quinoneimine and azomethine dyes, saidnucleus, in an enol form, having the formula:

(3) an addition polymerizable vinyl compound that is liquid at 50 C.,the gelatin, monomeric color former and polymerizable non-color formingmonomer being present in parts by weight of 10 to 90, 3 to 75, and 2 to60, respectively.

2. A process as set forth in claim 1 wherein the addition polymerizablenon-color former is an alkyl acrylate wherein the alkyl radical contains1 to 8 carbon atoms.

3. A process as set forth in claim 1 wherein the addition polymerizablenon-color former is an alkyl methacrylate wherein the alkyl radicalcontains 1 to 8 carbon atoms.

4. The color formers obtained by the process of claim 1.

References Cited UNITED STATES PATENTS 2,548,520 4/1951 Damschrodel' eta1. 2,763,625 9/1956 Illingsworth et a1. 2,956,884 10/ 1960 Cardwell2,976,294 3/ 1961 Firestine 3,211,552 10/1965 Chue 3,070,442 12/1962Cohen et a1.

WILLIAM H. SHORT, Primary Examiner.

E. M. WOODBERRY, Assistant Examinr.

US. Cl. X.R. 96-114; 260-117

